Examples that have been provided to date as treatment for articular cartilage defects include medical treatment (such as internal medicine or joint injection) and surgical treatment (such as microfracture, mosaicplasty, or cultured cartilage transplantation). Surgical treatment requires a patient to undergo rehabilitation for restoration to usual life. It is known that, during rehabilitation, an external brace is attached to the joint to reduce the load on a treated cartilage portion. For example, PTL 1 discloses an external brace that includes a first pin, attached to a first bone portion, a second pin, attached to a second bone portion, a first magnet portion, including a first permanent magnet and attached to the first pin, and a second magnet portion, including a second permanent magnet and attached to the second pin. The first magnet portion includes a protrusion having an arcuately protruding shape in a section taken in the direction perpendicular to the longitudinal direction of the first pin. The second magnet portion includes a recess having an arcuately recessed shape in a section taken in the direction perpendicular to the longitudinal direction of the second pin. The first magnet portion and the second magnet portion are disposed so that the protrusion and the recess face each other and the same poles of the first permanent magnet and the second permanent magnet face each other. Specifically, a cylindrical magnet is prepared as the first magnet portion and a magnet having a shape obtained by cutting an arcuate portion out of a surface of a rectangular parallelepiped is prepared as the second magnet portion. The cylindrical first magnet portion is disposed so as to face the arcuate surface of the second magnet portion. Such an external brace allows the first bone portion and the second bone portion to be spaced apart from each other using repulsive force between the magnets, so that the joint is allowed to move smoothly while the load on the treated cartilage portion is being lightened (in the state where the joint cavity is expanded).